Density Functional Perturbation Theory Research Articles

Mixed (NH4)2Mn0.47Cu0.53(SO4)2(H2O)6 Tutton salt: A novel optical material for solar-blind technology

In this paper, a novel mixed Tutton salt (NH4)2Mn0.47Cu0.53(SO4)2(H2O)6 obtained in single crystal form is described. Their structural, thermal, electrical, and spectroscopic properties have been examined, and their possible uses are discussed. The salt crystallizes in a monoclinic symmetry (P21/c) and exhibits thermal stability between 300-333 K. Above this temperature, the crystal undergoes phase changes associated with dehydration and crystallization processes. 231 optical phonons distributed between 50 and 4000 cm–1, calculated through density functional perturbation theory, were used to accurately assign vibrational modes in experimental FT-IR and Raman spectra. Additional computational studies using Hirshfeld surfaces have revealed that H···O/O···H and H···H intermolecular contacts are crucial interactions for stabilizing the crystal lattice. Electrical characteristics (resistivity = 1160 MΩ·cm; capacitance = 3.6 pF) and optical data (bandgap = 4.27 eV) depict a typical behavior of nonpolar dielectric materials. UV-Vis-NIR transmittance spectrum has shown deep light blocking in the UV-C and Vis/NIR spectral regions and high transmittance levels (reaching 98.5%) in the UV-B/-A/Vis range. The photoresponse findings point out that (NH4)2Mn0.47Cu0.53(SO4)2(H2O)6 is a promising light-absorbing material for solar-blind photodetection devices operating in the 200-280 nm interval. The crystal as a bandpass filter (280-615 nm) or a cut-off filter (615-1000 nm) are also excellent prospects for application.

Theoretical insights into the ultrahigh piezoelectric performance of (BiFeO3)n/(BaTiO3)n (n = 1–5) superlattices

Perovskite structures have attracted extensive attention in microelectromechanical systems and nanoelectromechanical systems devices due to the high piezoelectric response and the low dielectric constant. The piezoelectric and dielectric properties of the tetragonal BiFeO3/BaTiO3 superlattices grown along the c-axis direction are investigated using density functional theory (DFT) and density functional perturbation theory. The calculated results demonstrate that the (BiFeO3)n/(BaTiO3)n (n = 1–5) superlattices exhibit a profoundly increased piezoelectric response compared to their bulk structures. The (BiFeO3)2/(BaTiO3)2 possesses the highest piezoelectric d33 of 697 pC/N among known lead-free perovskite systems. Furthermore, the (BiFeO3)2/(BaTiO3)2 superlattice possesses a low dielectric ɛ33, and its d33 at 2% tensile strain is 16 times larger than that of an unstrained equilibrium structure. This demonstrates that biaxial tensile strain significantly enhances the piezoelectric response. Combining the special quasirandom structure method with DFT, the structures of a 0.5BiFeO3–0.5BaTiO3 solid solution are predicted, and its calculated d33 is 58 pC/N, which is much smaller than that of a (BiFeO3)2/(BaTiO3)2 superlattice. The results suggest that the (BiFeO3)2/(BaTiO3)2 superlattice might be a potential candidate for nonvolatile random access memory, transducers and actuators, and nanoscale electronic devices.

Ca3[C2O5]2[CO3] is a pyrocarbonate which can be formed at p, T-conditions prevalent in the Earth’s transition zone

Understanding the fate of subducted carbonates is a prerequisite for the elucidation of the Earth’s deep carbon cycle. Here we show that the concomitant presence of Ca[CO3] with CO2 in a subducting slab very likely results in the formation of an anhydrous mixed pyrocarbonate, Ca3C2O52CO3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{\\rm{Ca}}}}}_{3}{\\left[{{{{\\rm{C}}}}}_{2}{{{{\\rm{O}}}}}_{5}\\right]}_{2}\\left[{{{{\\rm{CO}}}}}_{3}\\right]$$\\end{document}, at moderate pressure ( ≈ 20 GPa) and temperature ( ≈ 1500 K) conditions. We show that at these conditions Ca3C2O52CO3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{\\rm{Ca}}}}}_{3}{\\left[{{{{\\rm{C}}}}}_{2}{{{{\\rm{O}}}}}_{5}\\right]}_{2}\\left[{{{{\\rm{CO}}}}}_{3}\\right]$$\\end{document} can be obtained by reacting Ca[CO3] with CO2 in a laser-heated diamond anvil cell. The crystal structure was obtained from synchrotron-based single crystal X-ray diffraction data. Density Functional Perturbation Theory calculations in combination with experimental Raman spectroscopy results unambiguously confirmed the structural model. The crystal structure of Ca3C2O52CO3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{\\rm{Ca}}}}}_{3}{\\left[{{{{\\rm{C}}}}}_{2}{{{{\\rm{O}}}}}_{5}\\right]}_{2}\\left[{{{{\\rm{CO}}}}}_{3}\\right]$$\\end{document} is characterized by the presence of CO32−\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\left[{{{{\\rm{CO}}}}}_{3}\\right]}^{2-}$$\\end{document}- and C2O52−\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\left[{{{{\\rm{C}}}}}_{2}{{{{\\rm{O}}}}}_{5}\\right]}^{2-}$$\\end{document}-groups. The results presented here imply that the formation of Ca3C2O52CO3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{\\rm{Ca}}}}}_{3}{\\left[{{{{\\rm{C}}}}}_{2}{{{{\\rm{O}}}}}_{5}\\right]}_{2}\\left[{{{{\\rm{CO}}}}}_{3}\\right]$$\\end{document} needs to be taken into account when constructing models of the deep carbon cycle of the Earth.

Cavity Born-Oppenheimer approximation for molecules and materials via electric field response.

We present an abinitio method for computing vibro-polariton and phonon-polariton spectra of molecules and solids coupled to the photon modes of optical cavities. We demonstrate that if interactions of cavity photon modes with both nuclear and electronic degrees of freedom are treated on the level of the cavity Born-Oppenheimer approximation, spectra can be expressed in terms of the matter response to electric fields and nuclear displacements, which are readily available in standard density functional perturbation theory implementations. In this framework, results over a range of cavity parameters can be obtained without the need for additional electronic structure calculations, enabling efficient calculations on a wide range of parameters. Furthermore, this approach enables results to be more readily interpreted in terms of the more familiar cavity-independent molecular electric field response properties, such as polarizability and Born effective charges, which enter into the vibro-polariton calculation. Using corresponding electric field response properties of bulk insulating systems, we are also able to obtain the Γ point phonon-polariton spectra of two dimensional (2D) insulators. Results for a selection of cavity-coupled molecular and 2D crystal systems are presented to demonstrate the method.

Training machine learning interatomic potentials for accurate phonon properties

Abstract One of the major challenges in the development of universal machine learning interatomic potentials is accurately reproducing phonon properties. This issue appears to arise from the limitations of available datasets rather than the models themselves. To address this, we develop an extensive dataset of phonon calculations using density-functional perturbation theory. We then show how this dataset can be used to train neural-network force fields, by implementing the training and the prediction of force constants in periodic crystals. This approach improves the quality of phonon properties prediction while reducing the number of structures needed for neural network training. We demonstrate the efficiency of this method using two examples of ternary phase diagrams: Ti—Nb—Ta and Li—B—C. In both cases, neural network predictions for the energy and forces show a considerable improvement, while phonon properties are predicted with high precision for all structures across the entire phase diagrams.

Light-Induced Polaronic Crystals in Single-Layer Transition Metal Dichalcogenides.

Light-induced ordered states can emerge in materials after irradiation with ultrafast laser pulses. However, their prediction is challenging because the inverted band occupation confounds our chemical intuition. Hence, we use a recently developed constrained density functional perturbation theory approach to systematically screen single-layer transition metal dichalcogenides (TMDs) for light-induced ordered states. We demonstrate that all examined single-layer TMDs reveal similar light-induced charge orderings. The corresponding reconstructions are periodic arrangements of polarons (polaronic crystals), characterized by triangular metal clusters and having no equivalent at equilibrium conditions. The polarons are accompanied by localized midgap states in the electronic band structure, detectable by experimental methods. We assess the selenides as the most promising candidates for potential photoexcitation experiments because they transition at low critical fluences, have low transition barriers, and maintain an open band gap under photoexcitation. Our work paves the way for innovative material design approaches targeting light-induced phases.

Understanding the optoelectronic and vibrational properties of MB[formula omitted]O[formula omitted], using density functional theory, where M = Yb or Ce

This work aims to use density functional theory (DFT) and density functional perturbation theory (DFPT) to study the structure, optoelectronics, phonon dispersion and energetic stability of two new tetraborates, MB4O7, where M = Yb or Ce. The estimated values of the band gap energy (Eg) and power conversion efficiency (PCE) for the systems were calculated. The Shockley-Queisser was also taken into account to measure the maximum theoretical efficiency of a photovoltaic source cell based on a p-n union. The estimated average gap energy values for the YbB4O7 and CeB4O7 systems, calculated using the GGA-PBE, HSE06, and GGA+U functionals, were 3.64 eV and 0.97 eV, respectively. The average PCEs calculated for the YbB4O7 and CeB4O7 systems were 11.28% and 25.66%, respectively. The PCE and energy stability suggest that CeB4O7 may be a more viable candidate for a solar device than YbB4O7, at least in terms of these specific parameters. The results reported here, as well as those related to absorption calculations, showed that the structures have optical responses in the visible region, suggesting that both systems can be used as optoelectronic devices and in solar cell designs.

First-principles study on lanthanide dopants in BaTiO3

Using first-principles calculation based on density-functional theory and density-functional perturbation theory, the microscopic structure and dielectric properties of Lanthanide (Ln) doped BaTiO3 are investigated. The doped Ln atoms exhibit significant displacement from Ba sites for charge compensation, forming off-centered configurations. This displacement is more pronounced for elements with smaller ionic radii. The change in ionic dielectric constant is strongly correlated with Ln displacement and Ln ion radius. As Ln displacement (ionic radius) increases (decreases), Ln-doped BaTiO3 has a higher ionic dielectric constant. However, regardless of the Ln species, the added Ln reduces the ionic dielectric constant compared to pristine BaTiO3.

Density functional theory study on the electronic structures and piezoelectric properties of hydrogenated monolayer II-VI semiconductor XYH2 (X = Zn, Cd; Y = S, Se, Te)

Piezoelectric materials have been widely used in various fields such as sensing and energy catalysis. This paper primarily investigates the structural, electronic and piezoelectric properties of hydrogenated II-VI monolayer semiconductor XYH2 (X = Zn, Cd; Y = S, Se, Te) by density functional theory. Results reveal that XYH2 monolayers exhibit stable hexagonal structures and tunable bandgaps ranging from 3.27 eV to 4.30 eV. Density functional perturbation theory is employed to investigate the out-of-plane piezoelectric coefficients of XYH2 monolayers. CdSH2 exhibits a value of −1.8 pm/V of out-of-plane piezoelectric coefficients which surpasses typical piezoelectric materials such as bulk ZnS (0.076 pm/V), ZnO (0.21 pm/V), CdS (0.143 pm/V), CdSe (0.104 pm/V), BN (0.33 pm/V) and GaN (0.96 pm/V). Our results indicate that hydrogenated II-VI monolayers can be a new type of novel piezoelectric semiconductors and hold a potential application for the piezoelectric devices.

First principles study on the dielectric and infrared properties of single crystal Al3BC3

The dielectric and infrared vibrational properties of single crystal Al3BC3 were computed using density functional perturbation theory. Utilizing a group theory approach, the frequencies and vibrational modes of all the infrared active modes at the Brillouin zone center were determined. The study explored the dielectric function, infrared reflectivity, and Born effective charge of Al3BC3 in directions both parallel and perpendicular to the c-axis. The analysis of the Born effective charge confirmed the existence of strong covalent bonds between B and C, as well as ionic bonds between Al and C in Al3BC3 ceramics.

First-principle study on the structural, electronic and mechanical properties of High Entropy Alloy TiZrFeRu for hydrogen storage applications

High-entropy alloys are promising for hydrogen storage, especially in terms of their tunable hydrogen storage properties. Although several experimental studies, a fundamental and detailed atomistic comprehension of physical and electronic of the hydrogenation process is still lacking. This work investigated the structural, electronic and mechanical properties of TiZrFeRu high-entropy alloys (HEAs) using first-principle calculation. Indeed, we employed both density functional theory and density functional perturbation theory in the calculations with generalized gradient approximation and plane-waves pseudo-potential formalism. In addition, we used Virtual crystal approximation (VCA) to describe HEA as is well suited for predicting elastic properties. We have calculated relevant physical parameters, including lattice constants, elastic constants, elastic modulus, Poisson's ratio, Pugh's ratio, anisotropy factors and Vickers hardness..etc. Our calculated finding show that that TiZrFeRuH2 is mechanically stable and has a good ductility with a Pugh’s ratio (B/G) greater than 1.75. Lastly, we investigated and discussed electronic bandstructure, the total and partial electronic density of state. The results indicate that this compound exhibit a metallic character concentrated in a zone between -5 and 5 eV. The value of the Poisson ration (0.35) confirm again that this compound is metallic (for metal materials the Poisson ratio is above 0.25).

Investigation on the structural, elastic, electronic, thermodynamic, and vibrational properties of the full heusler Sc2XAl (X =Cd and Zn): An ab initio study

The structural, mechanical, electronic, thermodynamic, and phonon characteristics of Sc2CdAl and Sc2ZnAl in L21 phase were the main focuses on this investigation. The density of states (DOS) and electronic band spectra signify the metallic behavior of the L21 phase of both materials. The impact of atomic arrangement with respect to the Wyckoff sites on the mechanical stability were additionally studied. The elastic constants of Sc2CdAl and Sc2ZnAl alloys indicated that these alloys convened Born mechanical stability criteria. Using the density functional perturbation theory's first-principle linear response method, complete phonon spectra have been acquired. Moreover, the quasi-harmonic approximation, specific heat capacity at constant volume, the internal free energy, entropy, and vibrational free energy variations of Sc2CdAl and Sc2ZnAl as full Heusler alloys have been utilized in examination the change over the temperature between 0 and 800 K. Both alloys might find application in real industrial applications.

Unraveling the electronic properties in SiO2 under ultrafast laser irradiation

First-principles simulations were conducted to explore various electronic properties of crystalline SiO2 (α-quartz) under ultrafast laser irradiation. Employing Density Functional Perturbation Theory and the many-body (GW) approximation, we calculated the impact of thermally excited electrons on the electronic specific heat, electron pressure, effective mass, deformation potential, electron-phonon coupling and electron relaxation time of quartz, covering a wide range of electron temperatures, up to 100,000 K. We show that the electron-phonon relaxation time of highly-excited quartz becomes twice faster compared to low-excited states. The deformation potential, which dictates atomic displacement, has a non-monotonic behavior with a well-pronounced minimum at around 16,000 K (2.7 × 1021 cm−3 of excited electrons) where the bond ionicity of the Si-O starts decreasing followed by a cohesion loss at 35,000 K due to the pressure exerted by the excited electrons on the lattice. Consequently, our calculated data, illustrating the evolution of physical parameters, can facilitate simulations of laser-matter interactions and provide predictive insights into the behavior of quartz under experimental conditions.

DFT insight into the phase stability, optoelectronic, elastic, vibrational, and thermodynamic properties of metal chalcogenides RbKM (M = S, Se, Te) for energy harvesting technology

In this manuscript, the structural, optoelectronic, elastic, vibrational, and thermodynamic properties of RbKM (M = S, Se, Te) chalcogenides are explored via first principles approach. The estimated equilibrium lattice parameters a(c) through the TB-mBJ functional are 5.3876 Å (8.2810 Å), 5.2700 Å (8.6550 Å) and 5.2656 Å (8.7707 Å) for RbKS, RbKSe and RbKTe, respectively. The large value of the cohesive (Ecoh) and formation energy (Eform) reveals that all these compounds are stable at 0 K that may be difficult to decompose at ambient conditions. The direct band gap for RbKS, RbKSe and RbKTe is noted as 4.05 eV, 3.71 eV and 3.63 eV, respectively that is sufficient to declare them as semiconducting materials. So far as, the projected density of states (PDOS), pseudo electrons residing in d orbitals of the rubidium atoms contribute in the conduction region and p orbitals of chalcogen elements partake in the valence band. The optical parameters are determined by Kramers-Kronig relations. The elastic constants unveil that all compounds are mechanically stable and hold anisotropic nature. Here the vibrational properties of RbKM (M = S, Se, Te) are examined through Density functional perturbation theory (DFPT) technique. The Harmonic Approximation Method (HAM) is utilized to seek thermodynamic stability that is ensured due to the observance of negative free energy for all cases. Our theoretical outcomes for RbKM (M = S, Se, Te) can contribute significantly to amelioration for future research in devising optoelectronic and energy harvesting like appliances.

Roles of Nonadiabatic Processes, Reaction Mechanism, and Selectivity in Cu-Catalyzed [2 + 2] Photocycloaddition of Norbornene and Acetone to Oxetane.

Oxetane has been extensively studied for its applications in medicinal chemistry and as a reactive intermediate in synthesis. Experiments report a Cu-catalyzed [2 + 2] photocycloaddition of acetone and norbornene to oxetane, which is proposed to deviate from the conventional Paternò-Büchi reaction. However, its mechanism at the atomic level is not clear. In this study, we used a combination of multistate complete active space second-order perturbation theory (MS-CASPT2) and density functional theory to systematically investigate the reaction mechanism and elucidate the factors contributing to the diastereomeric selectivity. Initially, the formation of the TpCu(Norb) complex is achieved by strong interaction between tris(pyrazolyl)borate Cu(I) (TpCu) and norbornene in the ground state (S0). Upon photoexcitation, TpCu(Norb) eventually decays to the T1 state, in which TpCu(Norb) attacks acetone to initiate subsequent reactions and produces final endo- or exo-oxetane products. All these reactions initially involve the C-C bond formation in the T1 state thereto leading to a ring-opening intermediate. This intermediate then undergoes a nonradiative transition to the S0 state, producing a five-membered ring intermediate, from which the C-O bond is formed, leading to the experimentally dominant exo-product. In contrast, the endo-oxetane formation requires a rearrangement process after the C-C bond is formed because of the large steric effects. As a consequence, the different reaction pathways generating exo- and endo-products exhibit large differences in the free-energy barriers, which results in a diastereomeric selectivity observed experimentally. Additionally, the nonradiative transition is found to play an important role in facilitating these reaction steps. The present computational study provides valuable mechanistic insights into Cu-catalyzed photocycloaddition reactions.

(Invited) Extended Hubbard Functionals for Accurate Modeling of Li-Ion Battery Cathode Materials

Designing novel cathode materials for Li-ion batteries necessitates accurate first-principles predictions of their properties. Density-functional theory (DFT) employing standard (semi-)local functionals encounters challenges due to pronounced self-interaction errors within the partially filled d shells of transition-metal (TM) elements. Here, we demonstrate the efficacy of DFT with extended Hubbard functionals in accurately predicting the "digital" change in oxidation states of TM ions for mixed-valence phases at intermediate Li concentrations in phospho-olivine and spinel cathode materials. The resulting voltages exhibit remarkable agreement with experimental data [1,2].Our approach involves the use of onsite U and intersite V Hubbard parameters computed from density-functional perturbation theory with Lowdin-orthogonalized atomic orbitals, thus circumventing empirical factors [3,4]. Notably, the incorporation of intersite Hubbard V interactions proves indispensable for the precise prediction of thermodynamic quantities, particularly when electronic localization occurs amid inter-atomic orbital hybridization.Extending our investigation to vibrational spectroscopy, we calculate Raman spectra for these materials and find very good agreement with available experimental data [5]. Leveraging the robust and accurate computational framework based on extended Hubbard functionals, we embark on a high-throughput screening of Li-containing compounds, aiming to unveil novel and promising candidates for cathodes [6]. Our findings underscore the pivotal role of advanced DFT methodologies in advancing the discovery and design of high-performance battery materials.[1] I. Timrov, F. Aquilante, M. Cococcioni, N. Marzari, PRX Energy 1, 033003 (2022).[2] I. Timrov, M. Kotiuga, N. Marzari, Phys. Chem. Chem. Phys. 25, 9061 (2023).[3] I. Timrov, N. Marzari, M. Cococcioni, Phys. Rev. B 98, 045141 (2021).[4] I. Timrov, N. Marzari, M. Cococcioni, Phys. Rev. B 103, 085127 (2018).[5] L. Bastonero, N. Marzari, I. Timrov, in preparation.[6] C. Malica, L. Bastonero, M. Bercx, N. Marzari, I. Timrov, in preparation.

Spin-dependent interactions in orbital-density-dependent functionals: Noncollinear Koopmans spectral functionals

The presence of spin-orbit coupling or noncollinear magnetic spin states can have dramatic effects on the ground-state and spectral properties of materials, in particular on the band structure. Here, we develop noncollinear Koopmans-compliant functionals based on Wannier functions and density-functional perturbation theory, targeting accurate spectral properties in the quasiparticle approximation. Our noncollinear Koopmans-compliant theory involves functionals of four-component orbital densities that can be obtained from the charge and spin-vector densities of Wannier functions. We validate our approach on four emblematic nonmagnetic and magnetic semiconductors where the effect of spin-orbit coupling goes from small to very large: the III-IV semiconductor GaAs, the transition-metal dichalcogenide WSe2, the cubic perovskite CsPbBr3, and the ferromagnetic semiconductor CrI3. The predicted band gaps are comparable in accuracy to state-of-the-art many-body perturbation theory and include spin-dependent interactions and screening effects that are missing in standard diagrammatic approaches based on the random phase approximation. While the inclusion of orbital- and spin-dependent interactions in many-body perturbation theory requires self-screening or vertex corrections, they emerge naturally in the Koopmans-functionals framework. Published by the American Physical Society 2024

Structural, elastic, electronic, optical and anisotropy properties of newly quaternary Tl2HgGeSe4 via DFPT predictions associated to XPES and RS experiments

In the present work, we report on theoretical studies of thermodynamic properties, structural and dynamic stabilities, dependence of unit-cell parameters and elastic constants upon hydrostatic pressure, charge carrier effective masses, electronic and optical properties, contributions of interband transitions in the Brillouin zone of the novel Tl2HgGeSe4 crystal. The theoretical calculations within the framework of the density-functional perturbation theory (DFPT) are carried out employing different approaches to gain the best correspondence to the experimental data. The present theoretical data indicate the dynamical stability of the title crystal and they reveal that, under hydrostatic pressure, it is much more compressible along the a-axis than along the c-axis. Strikingly, the charge effective mass values (me∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$m_{e}^{{^{*} }}$$\\end{document} and mh∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$m_{h}^{{^{*} }}$$\\end{document}) vary considerably when the high symmetry direction changes indicating a relative anisotropy of the charge-carrier’s mobility. Furthermore, the Young modulus and compressibility are characterized by the maximum and minimum values (Emax\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E^{max}$$\\end{document} and Emin\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E^{\\min }$$\\end{document}) and (βmax\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta^{max}$$\\end{document} and βmin\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta^{\\min }$$\\end{document}) that are equal to (62.032 and 28.812) GPa and (13.672 and 6.7175) TPa–1, respectively. Additionally, we have performed calculations of the Raman spectra (RS) and reached a good correspondence with the experimental RS spectra of the Tl2HgGeSe4 crystal. The XPES associated to RS constitutes powerful techniques to explore the oxidized states of Se and Ge in Tl2HgGeSe4 system.

Second-harmonic generation tensors from high-throughput density-functional perturbation theory

Optical materials play a key role in enabling modern optoelectronic technologies in a wide variety of domains such as the medical or the energy sector. Among them, nonlinear optical crystals are of primary importance to achieve a broader range of electromagnetic waves in the devices. However, numerous and contradicting requirements significantly limit the discovery of new potential candidates, which, in turn, hinders the technological development. In the present work, the static nonlinear susceptibility and dielectric tensor are computed via density-functional perturbation theory for a set of 579 inorganic semiconductors. The computational methodology is discussed and the provided database is described with respect to both its data distribution and its format. Several comparisons with both experimental and ab initio results from literature allow to confirm the reliability of our data. The aim of this work is to provide a relevant dataset to foster the identification of promising nonlinear optical crystals in order to motivate their subsequent experimental investigation.

Intrinsic Limits of Charge Carrier Mobilities in Layered Halide Perovskites

Layered halide perovskites have emerged as potential alternatives to three-dimensional (3D) halide perovskites due to their improved stability and larger material phase space, allowing fine tuning of structural, electronic, and optical properties. However, their charge carrier mobilities are significantly smaller than those of 3D halide perovskites, which has a considerable impact on their application in optoelectronic devices. Here, we employ state-of-the-art approaches to unveil the electron-phonon mechanisms responsible for the diminished transport properties of layered halide perovskites. Starting from a prototypical AMX3 halide perovskite, we model the case of n=1 and n=2 layered structures and compare their electronic and transport properties to the 3D reference. The electronic and phononic properties are investigated within density functional theory (DFT) and density functional perturbation theory (DFPT), while transport properties are obtained via the Boltzmann transport equation. The vibrational modes contributing to charge carrier scattering are investigated and associated with polar-phonon scattering mechanisms arising from the long-range Fröhlich coupling and deformation-potential scattering processes. Our investigation reveals that the lower mobilities in layered systems primarily originate from the increased electronic density of states at the vicinity of the band edges, while the electron-phonon coupling strength remains similar. Such an increase is caused by the dimensionality reduction and the break in octahedra connectivity along the stacking direction. Our findings provide a fundamental understanding of the electron-phonon coupling mechanisms in layered perovskites and highlight the intrinsic limitations of the charge carrier transport in these materials. Published by the American Physical Society 2024